Ancient's Way is one of the levels you need to get through to reach the fifth quest, Rite of Passage, and later on, entry to the Worldstone Keep. In fact, once you advance to the Ancient's Way, the last ice caves level in the game, and then return to town, Qual-Kehk will be eager to talk to you about it.

He warns of the Ancients who are guarding the entry to the Worldstone Keep. You don't need to talk to Qual-Kehk or anyone about this, however. You can just advance through the Ancient's Way to the Arreat Summit, and do it. This quest seems straightforward, but has a very tricky element in Rite of Passage you see in no other quest in all of Diablo II...